Oxyfluoride glasses were developed with composition 60GeO 2 ·10AlF 3 ·25BaF 2 ·（1.95-x）GdF 3 · 3YbF 3 ·0.05TmF 3 ·xErF 3 （x=0.02,0.05,0.08,0.11,0.14,0.17）in mole percent.Intense blue...Oxyfluoride glasses were developed with composition 60GeO 2 ·10AlF 3 ·25BaF 2 ·（1.95-x）GdF 3 · 3YbF 3 ·0.05TmF 3 ·xErF 3 （x=0.02,0.05,0.08,0.11,0.14,0.17）in mole percent.Intense blue（476 nm）,green（524 and 546 nm）and red（658 nm）emissions which identified from the 1G 4 →3H 6 transition of Tm3＋and the（2H 11/2 ,4S 3/2 ）→4I 15/2 ,4F 9/2 →4I 15/2 transitions of Er3＋,respectively,were simultaneously observed under 980 nm excitation at room temperature.The results show that multicolor luminescence including white light can be adjustably tuned by changing doping concentrations of Er3＋ion or the excitation power.In addition,the energy transfer processes among Tm3＋,Er3＋and Yb3＋ions,and up-conversion mechanisms are discussed.展开更多
We theoretically demonstrate a model which can be used to analyze frequency up-conversion of a laser wavelength by using thermal population. The proposed model uses a rate equation model of ytterbium-doped fiber with ...We theoretically demonstrate a model which can be used to analyze frequency up-conversion of a laser wavelength by using thermal population. The proposed model uses a rate equation model of ytterbium-doped fiber with thermal population effect. The rate and power propagation equations are set up and numerically analyzed to elucidate the dependence of frequency up-conversion efficiency and thermal-optical conversion efficiency on ambient thermal power. The analytical techniques and numerical results show that using pump laser at 1 000 nm,the wavelength can be converted into 900 nm with an up-conversion quantum efficiency of about 99.97% and a cooling efficiency of about 11.1%. This theoretical model is a promising candidate for vast applications in energyefficient laser and energy-utilizing field.展开更多
The quantum state transfer from subharmonic frequency to harmonic frequency based on asymmetrically pumped second harmonic generation in a cavity is investigated theoretically. The performance of noise-free frequency ...The quantum state transfer from subharmonic frequency to harmonic frequency based on asymmetrically pumped second harmonic generation in a cavity is investigated theoretically. The performance of noise-free frequency up- conversion is evaluated by the signal transfer coefficient and the conversion efficiency, in which both the quadrature fluctuation and the average photon number are taken into consideration. It is shown that the quantum property can be preserved during frequency up-conversion via operating the cavity far below the threshold. The dependences of the transfer coefficient and the conversion efficiency on pump parameter, analysing frequency, and cavity extra loss are also discussed.展开更多
This paper presents a scheme for realizing the frequency up-conversion between two collective atomic modes. In the scheme two atomic samples are coupled to a cavity mode. Under the large detuning condition, the two co...This paper presents a scheme for realizing the frequency up-conversion between two collective atomic modes. In the scheme two atomic samples are coupled to a cavity mode. Under the large detuning condition, the two collective atomic modes are coupled via the virtual excitation of the cavity mode and the effective Hamiltonian corresponds to the frequency up-conversion. In the scheme the cavity mode is only virtually excited and thus the process is insensitive to cavity decay.展开更多
A study is made of the effects of Doppler broadening on pure gain without inversion, which means that neither one-photon nor two-photon inversions are allowed, and non-pure gain without inversion, which means that one...A study is made of the effects of Doppler broadening on pure gain without inversion, which means that neither one-photon nor two-photon inversions are allowed, and non-pure gain without inversion, which means that one-photon inversion does not occur but two-photon inversion is present, in a closed A-type three-level system with incoherent pumping. It is shown that when the driving field is resonant but the probe field is not, in a certain range of Doppler width, for the case of the lower degree of frequency up-conversion, generally, pure gain without inversion increases monotonically and non-pure gain without inversion does not monotonically increase or decrease with increasing Doppler width; for the case of the higher degree of frequency up-conversion, pure gain without inversion decreases monotonically but non-pure gain without inversion cannot be produced. In the case of two-photon resonance, in some range of Doppler width, pure gain without inversion does not monotonically increase or decrease while non-pure gain without inversion decreases monotonically with Doppler width increasing. Finally, an experimental scheme for examining our theoretical result is given.展开更多
A weak infrared （IR） image amplifier with more than 60-dB optical gain and is developed from a picosecond （PS） 355-nm pumped gated optical parametric frequency up-conversion amplifier （OPA） in a/% BaB204 （BBO）...A weak infrared （IR） image amplifier with more than 60-dB optical gain and is developed from a picosecond （PS） 355-nm pumped gated optical parametric frequency up-conversion amplifier （OPA） in a/% BaB204 （BBO） crystal. The IR image at 1064 nm is amplified and up-converted into the visible region at 532 nm by parametric amplification and up-conversion. With the optimized optical gain, the lowest detectable energy of the image can be as low as 1.8 femto-Joule per pulse, which is three orders of magnitude lower than the detection limit of a charge-coupled device （CCD） camera. The transversal resolution of the OPA imaging is investigated, and the approaches for higher detection sensitivity and higher transversal resolution are proposed.展开更多
Passive acoustic monitoring(PAM)technology is increasingly becoming one of the mainstream methods for bird monitoring.However,detecting bird audio within complex natural acoustic environments using PAM devices remains...Passive acoustic monitoring(PAM)technology is increasingly becoming one of the mainstream methods for bird monitoring.However,detecting bird audio within complex natural acoustic environments using PAM devices remains a significant challenge.To enhance the accuracy(ACC)of bird audio detection(BAD)and reduce both false negatives and false positives,this study proposes a BAD method based on a Dual-Feature Enhancement Fusion Model(DFEFM).This method incorporates per-channel energy normalization(PCEN)to suppress noise in the input audio and utilizes mel-frequency cepstral coefficients(MFCC)and frequency correlation matrices(FCM)as input features.It achieves deep feature-level fusion of MFCC and FCM on the channel dimension through two independent multi-layer convolutional network branches,and further integrates Spatial and Channel Synergistic Attention(SCSA)and Multi-Head Attention(MHA)modules to enhance the fusion effect of the aforementioned two deep features.Experimental results on the DCASE2018 BAD dataset show that our proposed method achieved an ACC of 91.4%and an AUC value of 0.963,with false negative and false positive rates of 11.36%and 7.40%,respectively,surpassing existing methods.The method also demonstrated detection ACC above 92%and AUC values above 0.987 on datasets from three sites of different natural scenes in Beijing.Testing on the NVIDIA Jetson Nano indicated that the method achieved an ACC of 89.48%when processing an average of 10 s of audio,with a response time of only 0.557 s,showing excellent processing efficiency.This study provides an effective method for filtering non-bird vocalization audio in bird vocalization monitoring devices,which helps to save edge storage and information transmission costs,and has significant application value for wild bird monitoring and ecological research.展开更多
Although eye problems can occur at any age, they are often common from the age of 40. Eye diseases with a prevalence associated with age and aging will continue to increase in the coming years. Most studies conducted ...Although eye problems can occur at any age, they are often common from the age of 40. Eye diseases with a prevalence associated with age and aging will continue to increase in the coming years. Most studies conducted on problems in middle-aged people have focused on visual disorders without taking into account all the ocular morbidities that may affect this segment of the population, hence the present study, the aim of which is to determine the proportions of different eye diseases in people aged 40 and over. Materials and Methods: This was a descriptive cross-sectional study carried out in the ophthalmology department covering the period from January 1 to December 31, 2020. Results: In total, we collected 828 patients aged 40 and over out of 1811 patients who received ophthalmological consultation during the study period, representing 45.72%. The most represented age group was 40 - 50 years, with an average age of 58.84 years and a maximum of 93 years. There were slightly more women (62.3%) than men (37.7%). The main reasons for consultation were decreased visual acuity (26.4%) and pruritus (19.9%). The main eye diseases diagnosed were cataracts (23%), allergic conjunctivitis (21.1%), and bacterial conjunctivitis (14.2%). Discussions: The predominance of cataracts in the diagnosed diseases confirms the literature data, according to which the main eye morbidities in middle-aged and elderly people are cataracts, glaucoma, and age-related macular degeneration. Conclusion: It is crucial to have a mastery of these epidemiological data of eye diseases in order to adapt the technical platforms of eye care structures to the needs of different segments of the population.展开更多
The frequency regulation reserve setting of wind-PV-storage power stations is crucial.However,the existing grid codes set up the station reserve in a static manner,where the synchronous generator characteristics and f...The frequency regulation reserve setting of wind-PV-storage power stations is crucial.However,the existing grid codes set up the station reserve in a static manner,where the synchronous generator characteristics and frequency-step disturbance scenario are considered.Thus,the advantages of flexible regulation of renewable generations are wasted,resulting in excessive curtailment of wind and solar resources.In this study,a method for optimizing the frequency regulation reserve of wind PV storage power stations was developed.Moreover,a station frequency regulation model was constructed,considering the field dynamic response and the coupling between the station and system frequency dynamics.Furthermore,a method for the online evaluation of the station frequency regulation was proposed based on the benchmark governor fitting.This method helps in overcoming the capacity-based reserve static setting.Finally,an optimization model was developed,along with the proposal of the linearized solving algorithm.The field data from the JH4#station in China’s MX power grid was considered for validation.The proposed method achieves a 24.77%increase in the station income while ensuring the system frequency stability when compared with the grid code-based method.展开更多
To develop new up-conversion luminescent materials for non-contact optical thermometer with high sensitivity and temperature re solution,a battery of KBaGd(MoO_(4))_(3):Yb^(3+),Ho^(3+)phosphors were fabricated through...To develop new up-conversion luminescent materials for non-contact optical thermometer with high sensitivity and temperature re solution,a battery of KBaGd(MoO_(4))_(3):Yb^(3+),Ho^(3+)phosphors were fabricated through solid reaction process.The crystal structure,up-conversion luminescence,energy transfer,thermal stability and optical temperature sensing performances were studied in detail.Under 980 nm laser excitation,the KBaGd(MoO_(4))_(3):Yb^(3+),Ho^(3+)phosphor exhibits distinctive emission bands of Ho^(3+)at545,660,and 755 nm,and excellent illuminant performance.Based on the thermally coupled levels(TCLs)of Ho^(3+),both the relative sensitivity(S_(r))and absolute sensitivity(S_(a))display similar change trends,with the highest values of 6.73%/K(@298 K)and 5.69%/K(@298 K),respectively.Furthermore,the highest Saof 13.90%/K(@623 K)and the ultimate Srof 0.62%/K(@298 K)are achieved based on non-TCLs of Ho^(3+).Therefore,KBaGd(MoO_(4))_(3):Yb^(3+),Ho^(3+)phosphor is a promising candidate for self-referenced optical thermometry.展开更多
As the development of new power systems progresses,the inherent inertia of power systems continues to diminish.Centralized frequency regulation,which relies on rapid communication and real-time control,can enable inve...As the development of new power systems progresses,the inherent inertia of power systems continues to diminish.Centralized frequency regulation,which relies on rapid communication and real-time control,can enable inverter-based thermostatically controlled load(ITCL)clusters to provide virtual inertia support to the power grid.However,ITCL clusters exhibit significant discrete response characteristics,which precludes the direct integration of load-side inertia support into the synchronous unit side.To address this issue,this paper elaborates on the existing technical framework and analyzes the underlying causes of the problem.It proposes a timestamp allocation mechanism for ITCL cluster control instructions,ensuring that many ITCL terminals can be triggered at staggered times,thereby allowing the load cluster power to adhere to the inertia analog control law at any moment.Building on this foundation,the paper further examines the impact of the inertia response delay of ITCL clusters,which is based on centralized frequency regulation,on the stability of the power system.A design scheme for inertia analog control parameters is proposed,taking into account dual constraints,frequency stability and load cluster regulation capacity.Finally,the feasibility and applicability of the proposed mechanism and parameter design scheme are investigated through simulations conducted via MATLAB/Simulink.展开更多
In this paper,a linear optimization method(LOM)for the design of terahertz circuits is presented,aimed at enhancing the simulation efficacy and reducing the time of the circuit design workflow.This method enables the ...In this paper,a linear optimization method(LOM)for the design of terahertz circuits is presented,aimed at enhancing the simulation efficacy and reducing the time of the circuit design workflow.This method enables the rapid determination of optimal embedding impedance for diodes across a specific bandwidth to achieve maximum efficiency through harmonic balance simulations.By optimizing the linear matching circuit with the optimal embedding impedance,the method effectively segregates the simulation of the linear segments from the nonlinear segments in the frequency multiplier circuit,substantially improving the speed of simulations.The design of on-chip linear matching circuits adopts a modular circuit design strategy,incorporating fixed load resistors to simplify the matching challenge.Utilizing this approach,a 340 GHz frequency doubler was developed and measured.The results demonstrate that,across a bandwidth of 330 GHz to 342 GHz,the efficiency of the doubler remains above 10%,with an input power ranging from 98 mW to 141mW and an output power exceeding 13 mW.Notably,at an input power of 141 mW,a peak output power of 21.8 mW was achieved at 334 GHz,corresponding to an efficiency of 15.8%.展开更多
To explore the electrostatic discharge behavior of charged powders in industrial silos,discharge experiments are conducted based on a full-size industrial silo discharge platform.Electrostatic discharge mode,frequency...To explore the electrostatic discharge behavior of charged powders in industrial silos,discharge experiments are conducted based on a full-size industrial silo discharge platform.Electrostatic discharge mode,frequency,and energy are investigated for powders of different polarities.Although the powders have low charge-to-mass ratios(+0.087μC/kg for the positively charged powders and−0.26μC/kg for the negatively charged ones),electrostatic discharges occur approximately every 10 s,with the maximum discharge energy being 800 mJ.Powder polarity considerably influences discharge energy.The positive powders exhibit higher discharge energy than the negative ones,although discharge frequency remains similar for both.Effects of powder charge,humidity,and mass flow on discharge frequency and discharge energy are quantitatively analyzed,providing important insights for the improvement of safety in industrial powder handling.展开更多
Delineation of hydrocarbon-bearing sands and the extent of accumulation using seismic data is a reoccurring challenge for many fields.This study addressed the existing challenges of delineating a known hydrocarbon reg...Delineation of hydrocarbon-bearing sands and the extent of accumulation using seismic data is a reoccurring challenge for many fields.This study addressed the existing challenges of delineating a known hydrocarbon region for a thin-pay reservoir using conventional attributes extraction methods.The efficacy of applying iso-frequency extraction and spectral frequency blending in identifying thin-pay and thick-pay reservoirs on seismic was tested by utilizing 3D seismic data and well logs data of Terra field in the Western Niger Delta Basin.Well tops of all the reservoirs in the field were picked and two reservoirs that correspond to thin-and thick-pay reservoirs,namely A and F were identified respectively.The gross pay thickness of reservoir A is 18 ft while that of reservoir F is 96 ft.Conventional attribute extraction such as RMS amplitude,minimum amplitude,and average energy can be used to identify the hydrocarbon-bearing region in reservoir F but was not applicable for identifying the thin-pay reservoir A.This prompted the interest of using iso-frequency extractions and spectral frequency blending of three iso-frequency cubes of 12 Hz,30 Hz,and 70 Hz to get a spectral frequency RGB cube.The 12 Hz isofrequency can be used to partially identify hydrocarbon-bearing region in reservoir A while the 30Hz iso-frequency can be used to partially identify hydrocarbon-bearing region in reservoir F.The results show that time slices from the spectral frequency blended cube were able to delineate both the thin-pay and thick-pay hydrocarbon-bearing regions as high amplitude.The extractions also conformed to the structure of the two reservoirs.However,there seems to be a color difference in the amplitude display for both reservoirs.The thick-pay reservoir showed a red color on the time slice while the thin-pay reservoir showed a green color.This study has shown that spectral frequency blending is a more effective tool than conventional attributes extractions in identifying hydrocarbon-bearing region using seismic data.The methodology utilized in this study can be applied to other fields with similar challenges and for identifying prospective hydrocarbon bearing areas.展开更多
Recently,many Sequential Recommendation methods adopt self-attention mechanisms to model user preferences.However,these methods tend to focus more on low-frequency information while neglecting highfrequency informatio...Recently,many Sequential Recommendation methods adopt self-attention mechanisms to model user preferences.However,these methods tend to focus more on low-frequency information while neglecting highfrequency information,which makes them ineffective in balancing users’long-and short-term preferences.At the same time,manymethods overlook the potential of frequency domainmethods,ignoring their efficiency in processing frequency information.To overcome this limitation,we shift the focus to the combination of time and frequency domains and propose a novel Hybrid Time-Frequency Dual-Branch Transformer for Sequential Recommendation,namely HyTiFRec.Specifically,we design two hybrid filter modules:the learnable hybrid filter(LHF)and the window hybrid filter(WHF).We combine these with the Efficient Attention(EA)module to form the dual-branch structure to replace the self-attention components in Transformers.The EAmodule is used to extract sequential and global information.The LHF andWHF modules balance the proportion of different frequency bands,with LHF globally modulating the spectrum in the frequency domain and WHF retaining frequency components within specific local frequency bands.Furthermore,we use a time domain residual information addition operation in the hybrid filter module,which reduces information loss and further facilitates the hybrid of time-frequency methods.Extensive experiments on five widely-used real-world datasets show that our proposed method surpasses state-of-the-art methods.展开更多
Cross-regional high voltage direct current(HVDC)systems bring remarkable renewable power injections to the receiver side of power grids.However,HVDC failures result in large disturbances to receivers and cause critica...Cross-regional high voltage direct current(HVDC)systems bring remarkable renewable power injections to the receiver side of power grids.However,HVDC failures result in large disturbances to receivers and cause critical frequency security problems.High renewable energy penetration also reduces the system inertia and damping coefficients.Thus,some nodal frequency nadirs may be much lower than those calculated by the center-of-inertia(COI)and may trigger low-frequency protection.Energy storage is a promising solution for frequency-related problems.In this study,we build an energy storage planning model considering both COI and nodal frequency security constraints.The energy storage capacities and locations are determined in the planning scheme based on year-round operations.First,we carry out a year-round COI-frequency-constrained unit commitment to obtain comprehensive operation modes.Next,we propose a hybrid data-model driven approach to generate nodal frequency security constraints for extensive operation modes effectively.Finally,we achieve optimal energy storage planning with both COI and nodal frequency constraints.Case studies on a modified RTS-79 test system and a 1089-bus power system in practical in Jiangsu,China,verify the effectiveness of the proposed methods.展开更多
Vibration detection using sensors with both wide working frequency range,good sensitivity,and other good performances is a topic of great interest in fields such as inertial navigation,deep-sea fishing boat engines co...Vibration detection using sensors with both wide working frequency range,good sensitivity,and other good performances is a topic of great interest in fields such as inertial navigation,deep-sea fishing boat engines condition monitoring,seismic monitoring,attitude,and heading reference system,etc.This paper investigates two 6H-SIC MEMS diaphragms,one triangular and the other square,used in a fiber optic Fabry–Perot(FP)accelerometer in an experimental scenario.The triangular chip shows a wide working frequency range of 630 Hz–5300 Hz,a natural frequency of 44.3 k Hz,and a mechanical sensitivity of 0.154 nm/g.An optimal structure of the square chip used in a probe such as a fiber optic FP accelerometer also shows a wide working frequency range of 120 Hz–2300 Hz;a good sensitivity of 31.5 m V/g,a resonance frequency of7873 Hz,an accuracy of 0.96%F.S.,a frequency measurement error of 1.15%,and an excellent linearity of 0.9995.展开更多
The usage characteristics of the large numerals in child language reflects both linguistic and cognitive development.The present study systematically examined Mandarin children’s naturalistic use of large numerals“...The usage characteristics of the large numerals in child language reflects both linguistic and cognitive development.The present study systematically examined Mandarin children’s naturalistic use of large numerals“bai”,“qian”,and“wan”and compared it with adult usage patterns based on a self-constructed corpus.The results revealed a significant preference for the use of“bai”over both“qian”and“wan”among children and adults alike.This shared pattern suggests that children’s acquisition of large numerals is strongly shaped by adult language input.This study addresses a critical gap in research on the acquisition of large numerals by Mandarin-speaking children,providing valuable insights for the broader theoretical framework of cross-linguistic numerical cognition.展开更多
Semantic segmentation of novel object categories with limited labeled data remains a challenging problem in computer vision.Few-shot segmentation methods aim to address this problem by recognizing objects from specifi...Semantic segmentation of novel object categories with limited labeled data remains a challenging problem in computer vision.Few-shot segmentation methods aim to address this problem by recognizing objects from specific target classes with a few provided examples.Previous approaches for few-shot semantic segmentation typically represent target classes using class prototypes.These prototypes are matched with the features of the query set to get segmentation results.However,class prototypes are usually obtained by applying global average pooling on masked support images.Global pooling discards much structural information,which may reduce the accuracy of model predictions.To address this issue,we propose a Category-Guided Frequency Modulation(CGFM)method.CGFM is designed to learn category-specific information in the frequency space and leverage it to provide a twostage guidance for the segmentation process.First,to self-adaptively activate class-relevant frequency bands while suppressing irrelevant ones,we leverage the Dual-Perception Gaussian Band Pre-activation(DPGBP)module to generate Gaussian filters using class embedding vectors.Second,to further enhance category-relevant frequency components in activated bands,we design a Support-Guided Category Response Enhancement(SGCRE)module to effectively introduce support frequency components into the modulation of query frequency features.Experiments on the PASCAL-5^(i) and COCO-20^(i) datasets demonstrate the promising performance of our model.展开更多
This study can play an important role in addressing the issue of achieving stable controlof launch vehicles when the first-order elastic frequency is near or overlaps with the rigid-body fre-quency,especially without ...This study can play an important role in addressing the issue of achieving stable controlof launch vehicles when the first-order elastic frequency is near or overlaps with the rigid-body fre-quency,especially without prior frequency knowledge.Much of the research up to now,such asthose based on notch-filter or signal-processing techniques,requires a gap of 3 to 5 times betweenthe low-order elastic frequencies and the rigid-body cutoff frequency.Observer-based methods,onthe other hand,require prior knowledge of the frequency data.In this paper,a method is proposed,which takes advantage of the fact that attitude measurements of the rigid-body,obtained by InertialMeasurement Units(IMUs)installed at different locations,are identical,whereas elastic-mode sig-nals differ only in their modal slopes.By differentially processing these IMU measurements,we canextract only the elastic information,thus identifying the frequencies of the elastic modes,and designan observer to distinguish the first-order elastic signal using redundant measurements.Simulationsdemonstrate that this method can autonomously identify low-order elastic frequencies,even whenthey are identical to or less than the rigid-body frequency,thereby enhancing controller perfor-mance.展开更多
基金Funded by the National Natural Science Foundation of China (No. 50772045)the Society Development Foundation of Yunnan Province (No. 2007E036M)
文摘Oxyfluoride glasses were developed with composition 60GeO 2 ·10AlF 3 ·25BaF 2 ·（1.95-x）GdF 3 · 3YbF 3 ·0.05TmF 3 ·xErF 3 （x=0.02,0.05,0.08,0.11,0.14,0.17）in mole percent.Intense blue（476 nm）,green（524 and 546 nm）and red（658 nm）emissions which identified from the 1G 4 →3H 6 transition of Tm3＋and the（2H 11/2 ,4S 3/2 ）→4I 15/2 ,4F 9/2 →4I 15/2 transitions of Er3＋,respectively,were simultaneously observed under 980 nm excitation at room temperature.The results show that multicolor luminescence including white light can be adjustably tuned by changing doping concentrations of Er3＋ion or the excitation power.In addition,the energy transfer processes among Tm3＋,Er3＋and Yb3＋ions,and up-conversion mechanisms are discussed.
基金the National Natural Science Foundation of China(Nos.60377023 and 60672017)the Program for New Century Excellent Talents in Universities(NCET)the Shanghai Optical Science and Technology Project(No.05DZ22009)
文摘We theoretically demonstrate a model which can be used to analyze frequency up-conversion of a laser wavelength by using thermal population. The proposed model uses a rate equation model of ytterbium-doped fiber with thermal population effect. The rate and power propagation equations are set up and numerically analyzed to elucidate the dependence of frequency up-conversion efficiency and thermal-optical conversion efficiency on ambient thermal power. The analytical techniques and numerical results show that using pump laser at 1 000 nm,the wavelength can be converted into 900 nm with an up-conversion quantum efficiency of about 99.97% and a cooling efficiency of about 11.1%. This theoretical model is a promising candidate for vast applications in energyefficient laser and energy-utilizing field.
基金Project supported by the National Natural Science Foundation of China (Grant No.10974126)the National Basic Research Program of China (Grant No.2010CB923102)
文摘The quantum state transfer from subharmonic frequency to harmonic frequency based on asymmetrically pumped second harmonic generation in a cavity is investigated theoretically. The performance of noise-free frequency up- conversion is evaluated by the signal transfer coefficient and the conversion efficiency, in which both the quadrature fluctuation and the average photon number are taken into consideration. It is shown that the quantum property can be preserved during frequency up-conversion via operating the cavity far below the threshold. The dependences of the transfer coefficient and the conversion efficiency on pump parameter, analysing frequency, and cavity extra loss are also discussed.
基金supported by the Doctoral Foundation of the Ministry of Education of China (Grant No 20070386002)
文摘This paper presents a scheme for realizing the frequency up-conversion between two collective atomic modes. In the scheme two atomic samples are coupled to a cavity mode. Under the large detuning condition, the two collective atomic modes are coupled via the virtual excitation of the cavity mode and the effective Hamiltonian corresponds to the frequency up-conversion. In the scheme the cavity mode is only virtually excited and thus the process is insensitive to cavity decay.
基金Project supported by the Natural Science Foundation of Shandong Province,China (Grant No Y2006A21)the National Natural Science Foundation of China (Grant No 10675076)
文摘A study is made of the effects of Doppler broadening on pure gain without inversion, which means that neither one-photon nor two-photon inversions are allowed, and non-pure gain without inversion, which means that one-photon inversion does not occur but two-photon inversion is present, in a closed A-type three-level system with incoherent pumping. It is shown that when the driving field is resonant but the probe field is not, in a certain range of Doppler width, for the case of the lower degree of frequency up-conversion, generally, pure gain without inversion increases monotonically and non-pure gain without inversion does not monotonically increase or decrease with increasing Doppler width; for the case of the higher degree of frequency up-conversion, pure gain without inversion decreases monotonically but non-pure gain without inversion cannot be produced. In the case of two-photon resonance, in some range of Doppler width, pure gain without inversion does not monotonically increase or decrease while non-pure gain without inversion decreases monotonically with Doppler width increasing. Finally, an experimental scheme for examining our theoretical result is given.
基金supported by the State Key Program for Basic Research of China(No.2010CB630706)the Knowledge Innovation Program of Chinese Academy of Sciences
文摘A weak infrared （IR） image amplifier with more than 60-dB optical gain and is developed from a picosecond （PS） 355-nm pumped gated optical parametric frequency up-conversion amplifier （OPA） in a/% BaB204 （BBO） crystal. The IR image at 1064 nm is amplified and up-converted into the visible region at 532 nm by parametric amplification and up-conversion. With the optimized optical gain, the lowest detectable energy of the image can be as low as 1.8 femto-Joule per pulse, which is three orders of magnitude lower than the detection limit of a charge-coupled device （CCD） camera. The transversal resolution of the OPA imaging is investigated, and the approaches for higher detection sensitivity and higher transversal resolution are proposed.
基金supported by the Beijing Natural Science Foundation(5252014)the National Natural Science Foundation of China(62303063)。
文摘Passive acoustic monitoring(PAM)technology is increasingly becoming one of the mainstream methods for bird monitoring.However,detecting bird audio within complex natural acoustic environments using PAM devices remains a significant challenge.To enhance the accuracy(ACC)of bird audio detection(BAD)and reduce both false negatives and false positives,this study proposes a BAD method based on a Dual-Feature Enhancement Fusion Model(DFEFM).This method incorporates per-channel energy normalization(PCEN)to suppress noise in the input audio and utilizes mel-frequency cepstral coefficients(MFCC)and frequency correlation matrices(FCM)as input features.It achieves deep feature-level fusion of MFCC and FCM on the channel dimension through two independent multi-layer convolutional network branches,and further integrates Spatial and Channel Synergistic Attention(SCSA)and Multi-Head Attention(MHA)modules to enhance the fusion effect of the aforementioned two deep features.Experimental results on the DCASE2018 BAD dataset show that our proposed method achieved an ACC of 91.4%and an AUC value of 0.963,with false negative and false positive rates of 11.36%and 7.40%,respectively,surpassing existing methods.The method also demonstrated detection ACC above 92%and AUC values above 0.987 on datasets from three sites of different natural scenes in Beijing.Testing on the NVIDIA Jetson Nano indicated that the method achieved an ACC of 89.48%when processing an average of 10 s of audio,with a response time of only 0.557 s,showing excellent processing efficiency.This study provides an effective method for filtering non-bird vocalization audio in bird vocalization monitoring devices,which helps to save edge storage and information transmission costs,and has significant application value for wild bird monitoring and ecological research.
文摘Although eye problems can occur at any age, they are often common from the age of 40. Eye diseases with a prevalence associated with age and aging will continue to increase in the coming years. Most studies conducted on problems in middle-aged people have focused on visual disorders without taking into account all the ocular morbidities that may affect this segment of the population, hence the present study, the aim of which is to determine the proportions of different eye diseases in people aged 40 and over. Materials and Methods: This was a descriptive cross-sectional study carried out in the ophthalmology department covering the period from January 1 to December 31, 2020. Results: In total, we collected 828 patients aged 40 and over out of 1811 patients who received ophthalmological consultation during the study period, representing 45.72%. The most represented age group was 40 - 50 years, with an average age of 58.84 years and a maximum of 93 years. There were slightly more women (62.3%) than men (37.7%). The main reasons for consultation were decreased visual acuity (26.4%) and pruritus (19.9%). The main eye diseases diagnosed were cataracts (23%), allergic conjunctivitis (21.1%), and bacterial conjunctivitis (14.2%). Discussions: The predominance of cataracts in the diagnosed diseases confirms the literature data, according to which the main eye morbidities in middle-aged and elderly people are cataracts, glaucoma, and age-related macular degeneration. Conclusion: It is crucial to have a mastery of these epidemiological data of eye diseases in order to adapt the technical platforms of eye care structures to the needs of different segments of the population.
基金supported by the Scientific Research Project of China Three Gorges Group Co.LTD(Contract Number:202103368).
文摘The frequency regulation reserve setting of wind-PV-storage power stations is crucial.However,the existing grid codes set up the station reserve in a static manner,where the synchronous generator characteristics and frequency-step disturbance scenario are considered.Thus,the advantages of flexible regulation of renewable generations are wasted,resulting in excessive curtailment of wind and solar resources.In this study,a method for optimizing the frequency regulation reserve of wind PV storage power stations was developed.Moreover,a station frequency regulation model was constructed,considering the field dynamic response and the coupling between the station and system frequency dynamics.Furthermore,a method for the online evaluation of the station frequency regulation was proposed based on the benchmark governor fitting.This method helps in overcoming the capacity-based reserve static setting.Finally,an optimization model was developed,along with the proposal of the linearized solving algorithm.The field data from the JH4#station in China’s MX power grid was considered for validation.The proposed method achieves a 24.77%increase in the station income while ensuring the system frequency stability when compared with the grid code-based method.
基金supported by the National Natural Science Foundation of China(61865003)。
文摘To develop new up-conversion luminescent materials for non-contact optical thermometer with high sensitivity and temperature re solution,a battery of KBaGd(MoO_(4))_(3):Yb^(3+),Ho^(3+)phosphors were fabricated through solid reaction process.The crystal structure,up-conversion luminescence,energy transfer,thermal stability and optical temperature sensing performances were studied in detail.Under 980 nm laser excitation,the KBaGd(MoO_(4))_(3):Yb^(3+),Ho^(3+)phosphor exhibits distinctive emission bands of Ho^(3+)at545,660,and 755 nm,and excellent illuminant performance.Based on the thermally coupled levels(TCLs)of Ho^(3+),both the relative sensitivity(S_(r))and absolute sensitivity(S_(a))display similar change trends,with the highest values of 6.73%/K(@298 K)and 5.69%/K(@298 K),respectively.Furthermore,the highest Saof 13.90%/K(@623 K)and the ultimate Srof 0.62%/K(@298 K)are achieved based on non-TCLs of Ho^(3+).Therefore,KBaGd(MoO_(4))_(3):Yb^(3+),Ho^(3+)phosphor is a promising candidate for self-referenced optical thermometry.
基金supported by the Key Scientific and Technological Projects(2024KJGG27)of Tianfu Yongxing Laboratorythe Experimental Platform Open Innovation Funding(209042025003)of Sichuan Energy Internet Research Institute,Tsinghua University.
文摘As the development of new power systems progresses,the inherent inertia of power systems continues to diminish.Centralized frequency regulation,which relies on rapid communication and real-time control,can enable inverter-based thermostatically controlled load(ITCL)clusters to provide virtual inertia support to the power grid.However,ITCL clusters exhibit significant discrete response characteristics,which precludes the direct integration of load-side inertia support into the synchronous unit side.To address this issue,this paper elaborates on the existing technical framework and analyzes the underlying causes of the problem.It proposes a timestamp allocation mechanism for ITCL cluster control instructions,ensuring that many ITCL terminals can be triggered at staggered times,thereby allowing the load cluster power to adhere to the inertia analog control law at any moment.Building on this foundation,the paper further examines the impact of the inertia response delay of ITCL clusters,which is based on centralized frequency regulation,on the stability of the power system.A design scheme for inertia analog control parameters is proposed,taking into account dual constraints,frequency stability and load cluster regulation capacity.Finally,the feasibility and applicability of the proposed mechanism and parameter design scheme are investigated through simulations conducted via MATLAB/Simulink.
基金Supported by the Beijing Municipal Science&Technology Commission(Z211100004421012),the Key Reaserch and Development Pro⁃gram of China(2022YFF0605902)。
文摘In this paper,a linear optimization method(LOM)for the design of terahertz circuits is presented,aimed at enhancing the simulation efficacy and reducing the time of the circuit design workflow.This method enables the rapid determination of optimal embedding impedance for diodes across a specific bandwidth to achieve maximum efficiency through harmonic balance simulations.By optimizing the linear matching circuit with the optimal embedding impedance,the method effectively segregates the simulation of the linear segments from the nonlinear segments in the frequency multiplier circuit,substantially improving the speed of simulations.The design of on-chip linear matching circuits adopts a modular circuit design strategy,incorporating fixed load resistors to simplify the matching challenge.Utilizing this approach,a 340 GHz frequency doubler was developed and measured.The results demonstrate that,across a bandwidth of 330 GHz to 342 GHz,the efficiency of the doubler remains above 10%,with an input power ranging from 98 mW to 141mW and an output power exceeding 13 mW.Notably,at an input power of 141 mW,a peak output power of 21.8 mW was achieved at 334 GHz,corresponding to an efficiency of 15.8%.
基金The National Natural Science Foundation of China(No.51976039)。
文摘To explore the electrostatic discharge behavior of charged powders in industrial silos,discharge experiments are conducted based on a full-size industrial silo discharge platform.Electrostatic discharge mode,frequency,and energy are investigated for powders of different polarities.Although the powders have low charge-to-mass ratios(+0.087μC/kg for the positively charged powders and−0.26μC/kg for the negatively charged ones),electrostatic discharges occur approximately every 10 s,with the maximum discharge energy being 800 mJ.Powder polarity considerably influences discharge energy.The positive powders exhibit higher discharge energy than the negative ones,although discharge frequency remains similar for both.Effects of powder charge,humidity,and mass flow on discharge frequency and discharge energy are quantitatively analyzed,providing important insights for the improvement of safety in industrial powder handling.
文摘Delineation of hydrocarbon-bearing sands and the extent of accumulation using seismic data is a reoccurring challenge for many fields.This study addressed the existing challenges of delineating a known hydrocarbon region for a thin-pay reservoir using conventional attributes extraction methods.The efficacy of applying iso-frequency extraction and spectral frequency blending in identifying thin-pay and thick-pay reservoirs on seismic was tested by utilizing 3D seismic data and well logs data of Terra field in the Western Niger Delta Basin.Well tops of all the reservoirs in the field were picked and two reservoirs that correspond to thin-and thick-pay reservoirs,namely A and F were identified respectively.The gross pay thickness of reservoir A is 18 ft while that of reservoir F is 96 ft.Conventional attribute extraction such as RMS amplitude,minimum amplitude,and average energy can be used to identify the hydrocarbon-bearing region in reservoir F but was not applicable for identifying the thin-pay reservoir A.This prompted the interest of using iso-frequency extractions and spectral frequency blending of three iso-frequency cubes of 12 Hz,30 Hz,and 70 Hz to get a spectral frequency RGB cube.The 12 Hz isofrequency can be used to partially identify hydrocarbon-bearing region in reservoir A while the 30Hz iso-frequency can be used to partially identify hydrocarbon-bearing region in reservoir F.The results show that time slices from the spectral frequency blended cube were able to delineate both the thin-pay and thick-pay hydrocarbon-bearing regions as high amplitude.The extractions also conformed to the structure of the two reservoirs.However,there seems to be a color difference in the amplitude display for both reservoirs.The thick-pay reservoir showed a red color on the time slice while the thin-pay reservoir showed a green color.This study has shown that spectral frequency blending is a more effective tool than conventional attributes extractions in identifying hydrocarbon-bearing region using seismic data.The methodology utilized in this study can be applied to other fields with similar challenges and for identifying prospective hydrocarbon bearing areas.
基金supported by a grant from the Natural Science Foundation of Zhejiang Province under Grant LY21F010016.
文摘Recently,many Sequential Recommendation methods adopt self-attention mechanisms to model user preferences.However,these methods tend to focus more on low-frequency information while neglecting highfrequency information,which makes them ineffective in balancing users’long-and short-term preferences.At the same time,manymethods overlook the potential of frequency domainmethods,ignoring their efficiency in processing frequency information.To overcome this limitation,we shift the focus to the combination of time and frequency domains and propose a novel Hybrid Time-Frequency Dual-Branch Transformer for Sequential Recommendation,namely HyTiFRec.Specifically,we design two hybrid filter modules:the learnable hybrid filter(LHF)and the window hybrid filter(WHF).We combine these with the Efficient Attention(EA)module to form the dual-branch structure to replace the self-attention components in Transformers.The EAmodule is used to extract sequential and global information.The LHF andWHF modules balance the proportion of different frequency bands,with LHF globally modulating the spectrum in the frequency domain and WHF retaining frequency components within specific local frequency bands.Furthermore,we use a time domain residual information addition operation in the hybrid filter module,which reduces information loss and further facilitates the hybrid of time-frequency methods.Extensive experiments on five widely-used real-world datasets show that our proposed method surpasses state-of-the-art methods.
基金supported in part by the National Natural Science Foundation of China(No.52177093)in part by the Scientific&technical project of China Electric Power Planning&Engineering Institute(K202317).
文摘Cross-regional high voltage direct current(HVDC)systems bring remarkable renewable power injections to the receiver side of power grids.However,HVDC failures result in large disturbances to receivers and cause critical frequency security problems.High renewable energy penetration also reduces the system inertia and damping coefficients.Thus,some nodal frequency nadirs may be much lower than those calculated by the center-of-inertia(COI)and may trigger low-frequency protection.Energy storage is a promising solution for frequency-related problems.In this study,we build an energy storage planning model considering both COI and nodal frequency security constraints.The energy storage capacities and locations are determined in the planning scheme based on year-round operations.First,we carry out a year-round COI-frequency-constrained unit commitment to obtain comprehensive operation modes.Next,we propose a hybrid data-model driven approach to generate nodal frequency security constraints for extensive operation modes effectively.Finally,we achieve optimal energy storage planning with both COI and nodal frequency constraints.Case studies on a modified RTS-79 test system and a 1089-bus power system in practical in Jiangsu,China,verify the effectiveness of the proposed methods.
基金Project supported by the National Natural Science Foundation of China(Grant No.32473216)Ningbo Youth Science and Technology Innovation Leading Talent Project(Grant No.2023QL004)。
文摘Vibration detection using sensors with both wide working frequency range,good sensitivity,and other good performances is a topic of great interest in fields such as inertial navigation,deep-sea fishing boat engines condition monitoring,seismic monitoring,attitude,and heading reference system,etc.This paper investigates two 6H-SIC MEMS diaphragms,one triangular and the other square,used in a fiber optic Fabry–Perot(FP)accelerometer in an experimental scenario.The triangular chip shows a wide working frequency range of 630 Hz–5300 Hz,a natural frequency of 44.3 k Hz,and a mechanical sensitivity of 0.154 nm/g.An optimal structure of the square chip used in a probe such as a fiber optic FP accelerometer also shows a wide working frequency range of 120 Hz–2300 Hz;a good sensitivity of 31.5 m V/g,a resonance frequency of7873 Hz,an accuracy of 0.96%F.S.,a frequency measurement error of 1.15%,and an excellent linearity of 0.9995.
文摘The usage characteristics of the large numerals in child language reflects both linguistic and cognitive development.The present study systematically examined Mandarin children’s naturalistic use of large numerals“bai”,“qian”,and“wan”and compared it with adult usage patterns based on a self-constructed corpus.The results revealed a significant preference for the use of“bai”over both“qian”and“wan”among children and adults alike.This shared pattern suggests that children’s acquisition of large numerals is strongly shaped by adult language input.This study addresses a critical gap in research on the acquisition of large numerals by Mandarin-speaking children,providing valuable insights for the broader theoretical framework of cross-linguistic numerical cognition.
文摘Semantic segmentation of novel object categories with limited labeled data remains a challenging problem in computer vision.Few-shot segmentation methods aim to address this problem by recognizing objects from specific target classes with a few provided examples.Previous approaches for few-shot semantic segmentation typically represent target classes using class prototypes.These prototypes are matched with the features of the query set to get segmentation results.However,class prototypes are usually obtained by applying global average pooling on masked support images.Global pooling discards much structural information,which may reduce the accuracy of model predictions.To address this issue,we propose a Category-Guided Frequency Modulation(CGFM)method.CGFM is designed to learn category-specific information in the frequency space and leverage it to provide a twostage guidance for the segmentation process.First,to self-adaptively activate class-relevant frequency bands while suppressing irrelevant ones,we leverage the Dual-Perception Gaussian Band Pre-activation(DPGBP)module to generate Gaussian filters using class embedding vectors.Second,to further enhance category-relevant frequency components in activated bands,we design a Support-Guided Category Response Enhancement(SGCRE)module to effectively introduce support frequency components into the modulation of query frequency features.Experiments on the PASCAL-5^(i) and COCO-20^(i) datasets demonstrate the promising performance of our model.
文摘This study can play an important role in addressing the issue of achieving stable controlof launch vehicles when the first-order elastic frequency is near or overlaps with the rigid-body fre-quency,especially without prior frequency knowledge.Much of the research up to now,such asthose based on notch-filter or signal-processing techniques,requires a gap of 3 to 5 times betweenthe low-order elastic frequencies and the rigid-body cutoff frequency.Observer-based methods,onthe other hand,require prior knowledge of the frequency data.In this paper,a method is proposed,which takes advantage of the fact that attitude measurements of the rigid-body,obtained by InertialMeasurement Units(IMUs)installed at different locations,are identical,whereas elastic-mode sig-nals differ only in their modal slopes.By differentially processing these IMU measurements,we canextract only the elastic information,thus identifying the frequencies of the elastic modes,and designan observer to distinguish the first-order elastic signal using redundant measurements.Simulationsdemonstrate that this method can autonomously identify low-order elastic frequencies,even whenthey are identical to or less than the rigid-body frequency,thereby enhancing controller perfor-mance.
